Datacenters have hardware, such as servers, hard disk drives, power supply units, and the like, that are air cooled. Multiple fans are often employed for cooling the associated hardware. Fan failure may result in failure of the associated hardware. Fans are field replaceable units (FRUs) that are frequently replaced in datacenters. The frequency of fan replacement is typically second only to hard disk drives, but not because hard disk drives are less reliable; rather, because there are many more hard disk drives in the systems than there are fans.
Because mechanical fans are high replacement units, most server products are designed so that the fans can be replaced in the field. If the fans fail completely, a field service engineer can typically visually detect which fan, or fan within a fan tray, has failed, thereby allowing the service engineer to replace the failed fan or fan tray. However, if a fan is experiencing degradation, but is still operational, it is extremely difficult to detect or undetectable by service engineers and customer datacenters. Often, fans that are suspected of potential degradation are removed from customer machines, replaced, shipped to a testing laboratory and tested in an attempt to distinguish degrading fans from undegraded fans. The testing involves putting the fans into an instrumented flow chamber to detect a difference in flow rate, typically by cubic feet per minute (CFM); and the performance is compared with normal, undegraded fans. Such testing is very costly.
It is difficult to distinguish degrading fans from undegraded fans in customer datacenters. Therefore, when a known degradation mode starts to appear for a given model of fans, it is typical for the system vendor to perform a worldwide recall. Such recalls have been launched when less than ten percent of the fans are effected by the degradation mode, simply because it is not detectable for field service engineers to distinguish degrading fans from undegraded fans. Such recalls can be extremely costly, even when the field replaceable units are only the fans. Power supply units are often deployed with internal fans that are not replaceable in the field. Therefore, during recalls, or during fan repair and/or replacement, the power supply units are replaced at substantial additional costs.